I do wonder if they might be slightly more careful in current times, as we might not actually be allowed to take that cheap Air Asia flight to Cambodia (etc) due to covid restrictions.
Of course, IF Christian's Cambodia visa is multi-entry, that is not a problem.
I don't recall anyone ever checking I have a flight out of Thailand.
I've had it when flying from Cebu to KL, but never to Thailand. Including the following day when I flew from KL to Utapao, with the same airline.